Most of the high-definition plasma televisions, liquid crystal televisions, digital projectors, DVD players and Blu-ray players that are available in the market today include high-definition multimedia interface (HDMI) connectors. By using an HDMI connector, a source device (e.g., a digital set-top box, a DVD player, a Blu-ray player, an HDD player or the like) can very reliably transfer digital content to a sink device (e.g., a high-definition television or display device, a digital projector, or the like).
The HDMI standard defines specifications to support any common high-definition formats, including 720p and 1080i high-definition televisions (HDTVs), which require a 1.5 Gbps data transfer rate (bit rate) with a bit error ratio (BER) of 10−9. Moreover, to ensure security while digital content is transferred between the source device and the sink device, the HDMI standard also defines specifications for the high-bandwidth digital content protection (HDCP) system. The HDMI standard thus comprehensively designed has wide support from the industry. As of 2008, the number of devices with HDMI sold was expected to increase from 50,000,000 in 2005 to more than 200,000,000.
FIG. 37 is a block diagram outlining signals to be transmitted from the source device to the sink device in accordance with the HDMI standard. FIG. 38 is a table showing signal types assigned to HDMI connector pins. First, the HDMI standard will be outlined with reference to FIGS. 37 and 38. Note that in FIG. 37, digital signals TMDS Data0+ and TMDS Data0− represent positive and negative polarities, respectively, of a differential signal. The above is similar for digital signals TMDS Data1+ and TMDS Data1− and also for digital signals TMDS Data2+ and TMDS Data2−.
A source device 900 and a sink device 901 are connected by an HDMI cable 902. Video and audio signals generated in the source device 900 are inputted to an HDMI transmitter 903. The HDMI transmitter 903 converts signals to be transmitted into a 3-channel serial digital signal before outputting to three channels, “TMDS Data0”, “TMDS Data1” and “TMDS Data2”, of the HDMI cable 902. For each of the channels “TMDS Data0”, “TMDS Data1” and “TMDS Data2”, the bit rate is up to 1485 Mbps (in the case of 1080P with a color depth of 8 bits). In addition, the HDMI transmitter 903 appropriately generates a clock signal TMDS CLK based on a control signal Control/Status, and outputs the generated signal to channel “TMDS Clock” of the HDMI cable 902. For example, “TMDS CLK” has a clock frequency one tenth of the bit rate for TMDS Data0 to TMDS Data2. An HDMI receiver 904 reproduces video and audio signals from the 3-channel serial digital signal inputted via the HDMI cable 902 using TMDS CLK, and then outputs the reproduced signals.
The source device 900 and the sink device 901 bi-directionally communicate SCL (serial clock) and SDA (serial data) as control signals referred to by DDC (display data channel). The control signals DDC are used to exchange settings and status information between the source device 900 and the sink device 901. For communication of the control signals DDC, a communication protocol called I2C (inter-integrated circuit) is used. The bit rate for I2C is as low as 100 Kbps.
The source device 900 and the sink device 901 use “Hot Plug Detect” and “+5V Power” pins in combination to confirm whether the HDMI cable is connected to the source device 900 and the sink device 901. The sink device 901 detects a +5V voltage outputted by the source device 900, thereby recognizing that the cable is connected thereto. The +5V voltage returns to “Hot Plug Detect” via a 1 kohm resistance within the sink device 901. The source device 900 recognizes the cable being connected thereto by detecting the “Hot Plug Detect” signal to be at 5V.
Note that CEC (consumer electronics control) refers to an optional control signal to be used for communication between the source device 900 and the sink device 901.
In this manner, the source device 900 and the sink device 901 are connected using the HDMI cable 902.
Incidentally, with the recent development of thinner and lighter HDTVs, wall-hanging HDTVs have come into the market. In the case of the wall-hanging HDTV, an HDMI cable being laid on the wall between the source device and the HDTV might compromise the appearance. Therefore, it is desirable that the source device and the HDTV wirelessly communicate with each other.
Under such circumstances, the following inventions have been proposed as described in Patent Documents 1 to 8.
Patent Document 1 describes a transmission device (1) in which a P/S (parallel-serial) conversion portion (10) converts R, G, B, and clock signals to a serial signal. Thereafter, in the transmission device (1), a serial-parallel converter (11) alternatingly branches the serial signal, resulting in I and Q signals. A QPSK modulation portion (12) of the transmission device (1) modulates the I signal with a millimeter wave to obtain an in-phase component (I1), and also modulates the Q signal with another millimeter wave 90 degrees out of phase to obtain a quadrature component (Q1). In the transmission device (1), an adder (12c) superimposes the in-phase component (I1) on the quadrature component (Q1) and outputs them via an antenna portion (13). A reception device (2) demodulates the superimposed signal (IQ1) transmitted from the transmission device (1). In this manner, Patent Document 1 discloses the transmission and reception devices by which digital signals are converted to a serial signal to be modulated by QPSK (quadrature phase shift keying) and wirelessly transmitted using a millimeter wave.
Patent Document 2 describes a multimedia source (12) with a first link (22) of 60 GHz and a second link of a lower rate. In the multimedia source (12), a forward channel modulator (36) modulates digital data into an analog signal using DQPSK (differential quadrature phase shift keying), QPSK, BPSK (binary phase shift keying), 8PSK (8-phase shift keying) or the like, and a forward channel upconverter (38) up-converts the signal to a 60-GHz millimeter wave for transmission.
Patent Document 3 describes a wireless transmission chip (16) in which a transmitter processor (18) converts multimedia data to I and Q signals, which are modulated by a wireless transmitter (20) using QPSK, DQPSK, BPSK, 8PSK or the like and then up-converted to a 60-GHz millimeter wave for transmission.
Patent Documents 4 to 8 describe wireless transmitters in which digital data is modulated using QPSK, DQPSK, BPSK, 8PSK or the like, and up-converted to a 60-GHz millimeter wave for transmission.
In addition, the following inventions as described in Non-Patent Documents 1 to 3 have been commercialized. Non-Patent Document 1 describes an invention sold at a street price of about ¥43,000, in which transmitter power consumption is 10 W, receiver power consumption is 12 W, transmitter external dimensions are about 190 (W)×70 (D)×69 (H) in mm, receiver external dimensions are about 146 (W)×46 (D)×133 (H) in mm, and SiBEAM's wireless technology WirelessHD is used.
Non-Patent Document 2 describes an invention sold at a street price of about US$999, in which transmitter power consumption is 12.5 W, receiver power consumption is 12.5 W, transmitter and receiver external dimensions are both about 6 (W)×4 (D)×2 (H) in inches, and Tzero Technologies' wireless technology ZeroWire is probably used.
Non-Patent Document 3 describes an invention sold at a street price of about ¥148,000, in which required power supply is 5 V/2.6 A, transmitter and receiver external dimensions are both 162.6 (W)×164.5 (D)×33.5 (H) in mm, and AMIMON's wireless technology WHDI (wireless home digital interface) is used.